20 are in Parshas Bo
4- To sanctify Rosh Chodesh , thus we learn that the Holidays are dependent on our Jewish Leaders.
We also see that time is to be utilized to serve Hashem.
5- We slaughter the Pesach offering the afternoon before Pesach. This is to show that we don't believe in foreign cultures & utilize everything to serve Hashem.
6- We eat the Korban Pesach the first night roasted.
7- not rare or cooked , only roasted.
8- No leftovers.
Now may be a good time for a gem of Torah study.